Separation of ionic liquid cations and related imidazole derivatives by α-cyclodextrin modified capillary zone electrophoresis

Abstract

The separation and detection of 1-alkyl-3-methylimidazolium, including isomers, and related imidazole derivatives was performed by alpha-cyclodextrin (alpha-CD) modified capillary zone electrophoresis. The separations were carried out in a running buffer comprising 5.0 mM triethylamine and 2.0 mM alpha-CD adjusted to pH 4.5 by acetic acid. All the analytes were baseline separated within 8 min and the detection limits (signal-to-noise ratio = 3) ranged between 0.42 and 1.36 ppm. The method showed good linearity (within 3-50 times the detection limits, r > 0.99) and reproducibility (relative standard deviation < 0.8% for migration times and < 3% for peak areas), which should make it suitable for routine analysis. It was employed in detecting impurities in commercial chemicals, and 0.27% 1-methylimidazole in 1-ethyl-3-methylimidazolium chloride and 0.55% imidazole in 2-ethylimidazole were found. In addition, it was employed in process analysis during synthesis of ionic liquids and demonstrated a potential to provide information on the reaction mechanism.